mflow reformats the standard input according
to the rules of RFC 3676. PIPE_CONTENTTYPE
is inspected, making this a suitable filter for ‘text/plain’
messages for mshow(1). Messages
not specified as ‘format=flowed’ are output unchanged.

Text is reflowed (where allowed) to fit the width given in the environment
variable COLUMNS, the terminal width, or 80
characters by default.

If defined, the environment variable
MAXCOLUMNS specifies the maximum line
length.